Thermally cured underlayer for lithographic application

ABSTRACT

Thermally cured undercoat for use in lithography of a thermally cured composition comprising a hydroxyl-containing polymer, an amino cross-linking agent and a thermal acid generator, wherein the hydroxyl containing polymer is a polymer comprising units m, n and o of the following formula:  
                 
 
     wherein R 1  is H or methyl; R 2  is a substituted or unsubstituted C 6 -C 14  aryl acrylate or C 6 -C 14  aryl methacrylate group wherein the substituted groups may be phenyl, C 1-4  alkyl or C 1-4  alkoxy; R 3  is a hydroxyl functionalized C 1 -C 8  alkyl acrylate, methacrylate or c 6 -C 14  aryl group, R 4  is a C 1 -C 10  linear or branched alkylene; p is an integer of from 1 to 5 with the proviso that there are no more than thirty carbon atoms in the [—R 4 O—] p ; R 5  is a C 1 -C 10  linear, branched or cyclic alkyl, substituted or unsubstituted C 6 -C 14  aryl, or substituted or unsubstituted C 7 -C 15  alicyclic hydrocarbon; and m is about 40 to 70, n is about 15 to 35 and o is about 15 to 25.

RELATED APPLICATION

[0001] This application is a continuation-in part of pending applicationSer. No. 09/901,933, filed Jul. 9, 2001, which in turn is a division ofapplication Ser. No. 09/268,430, filed Mar. 12, 1999, now U.S. Pat. No.6,323,287, issued Nov. 27, 2001.

FIELD OF THE INVENTION

[0002] The present invention relates to deep UV lithography used insemiconductor manufacturing and more particularly to undercoat layersfor chemically amplified bilayer resist systems.

BACKGROUND TO THE INVENTION

[0003] Integrated circuit production relies on the use ofphotolithographic processes to define the active elements andinterconnecting structures on microelectronic devices. Until recently,g-line (436 nm) and I-line (365 nm) wavelengths of light have been usedfor the bulk of microlithographic applications. However, in order toachieve smaller dimensions of resolution, the wavelength of light usedfor microlithography in semiconductor manufacturing has been reducedinto the deep UV regions of 254 nm and 193 nm. The problem with usingdeep UV wavelengths is that resists used at the higher wavelengths weretoo absorbent and insensitive. Thus, in order to utilize deep UV lightwavelengths, new resist materials with low optical absorption andenhanced sensitivities were needed.

[0004] Chemically amplified resist materials have recently beendeveloped through the use of acid-labile polymers in order to meet theabove-mentioned criteria. They have shown great promise in increasingresolution. However, chemically amplified resist systems have manyshortcomings. One problem is standing wave effects, which occur whenmonochromatic is reflected off the surface of a reflective substrateduring exposure. The formation of standing waves in the resist reducesresolution and causes linewidth variations. For example, standing wavesin a positive resist have a tendency to result in a foot at theresist/substrate interface reducing the resolution of the resist.

[0005] In addition, chemically amplified resist profiles and resolutionmay change due to substrate poisoning. Particularly, this effect occurswhen the substrate has a nitride layer. It is believed that residual N—Hbonds in the nitride film deactivates the acid at the nitride/resistinterface. For a positive resist, this results in an insoluble area, andeither resist scumming, or a foot at the resist/substrate interface.

[0006] Furthermore, lithographic aspect ratios require the chemicallyamplified resist layer be thin, e.g., about 0.5 μm or lower, to printsub 0.18 μm features. This in turn requires the resist to have excellentplasma etch resistance such that resist image features can betransferred down into the underlying substrate. However, in order todecrease absorbance of the chemically amplified resist, aromatic groups,such as those in novolaks had to be removed, which in turn decreased theetch resistance.

[0007] Utilizing an underlayer or undercoat film that is placed on thesubstrate before the chemical amplified film is applied can reduce theabove-mentioned problems. The undercoat absorbs most of the deep UVlight attenuating standing wave effects. In addition, the undercoatprevents deactivation of the acid catalyst at the resist/substrateinterface. Furthermore, the undercoat layer can contain some aromaticgroups to provide etch resistance.

[0008] In the typical bilayer resist process, the undercoat layer isapplied on the substrate. The chemically amplified resist is thenapplied on the undercoat layer, exposed to deep UV light and developedto form images in the chemically amplified resist topcoat. The bilayerresist system is then placed in an oxygen plasma etch environment toetch the undercoat in the areas where the chemically amplified resisthas been removed by the development. The chemically amplified resist ina bilayer system typically contains silicon and is thus able towithstand oxygen plasma etching by converting the silicon to silicondioxide, that then withstands the etch process. After the bottom layeris etched, the resist system can be used for subsequent processing suchas non-oxygen plasma etch chemistry that removes the underlyingsubstrate.

[0009] Even though the undercoat attenuates standing waves and substratepoisoning, it poses other problems. First, some undercoat layers aresoluble to the chemical amplified resist solvent component. If there isintermixing between the top and undercoat layers, the resolution andsensitivity of the top resist layer will be detrimentally affected.

[0010] In addition, if there is a large difference in the index ofrefraction between the chemical amplified resist and the undercoatlayer, light will reflect off the undercoat layer causing standing waveeffects in the resist. Thus, the real portion “n” of the index ofrefraction of the two layers must be made to essentially match or tohave their differences minimized, and the imaginary portion “k” of theindex of refraction of the two layers must be optimized to minimizereflectivity effects.

[0011] Another problem with undercoating layers is that they aresometimes too absorbent because of incorporation of aromatic groups.Some semiconductor manufacturing deep UV exposure tools utilize the samewavelength of light to both expose the resist and to align the exposuremask to the layer below the resist. If the undercoat layer is tooabsorbent, the reflected light needed for alignment is too attenuated tobe useful. However, if the undercoat layer is not absorbent enough,standing waves may occur. A formulator must balance these competingobjectives.

[0012] In addition, some undercoats have very poor plasma etchresistance to plasma chemistry. The etch resistance of the undercoatshould be comparable to the etch rate of novolak resins in order to becommercially viable.

[0013] Furthermore, some undercoat layers require UV exposure in orderto form cross-links before the radiation sensitive resist topcoat layercan be applied. The problem with UV cross-linking undercoat layers isthat they require long exposure times to form sufficient cross-links.The long exposure times severely constrain throughput and add to thecost of producing integrated circuits. The UV tools also do not provideuniform exposure so that some areas of the undercoat layer may becross-linked more than other areas of the undercoat layer. In addition,UV cross-linking exposure tools are very expensive and are not includedin most resist coating tools because of expense and space limitations.

[0014] Some undercoat layers are cross-linked by heating. However, theproblem with these undercoat layers is that they require high curingtemperatures and long curing times before the top layer can be applied.In order to be commercially useful, undercoat layers should be curableat temperatures below 250° C. and for a time less than 180 seconds.After curing, the undercoat should have a high glass transitiontemperature to withstand subsequent high temperature processing and notintermix with the resist layer.

[0015] Therefore, it has recently been proposed to utilize thermallycured undercoat layers in deep UV lithography utilizing compositionscontaining certain hydroxyl-functionalized polymers, thermal acidgenerating compounds and amine crosslinking agents. Thehydroxy-functionalized polymers proposed for use in such thermally curedunderlayer compositions have been copolymers of biphenyl methacrylate(BPMA) and 2-hydroxyethyl methacrylate (HEMA), generally employed with athermal acid generating compound (TAG) such as cyclohexyl tosylate andan amine crosslinking agent.

[0016] However, such proposed thermally cured undercoat (TCU)compositions have presented the following issues:

[0017] (a) solubility and compatibility of the current generation 248-nmTCU in common edge-bead removing (EBR) solvents such as propylene glycolmono methyl ether acetate (PGMEA), ethyl lactate (EL), ethyl ethoxypropionate (EEP), and the like;

[0018] (b) standing waves presumably, due to less than optimum match ofoptical parameters (n and k) of the undercoat with substrate and imaginglayer (IL); and

[0019] (c) scumming at the TCU/imaging layer (IL) interface.

[0020] In the proposed TCU compositions, although optical constants wereable to be reasonably matched, standing waves and scumming at the TCU/ILinterface could not be totally eliminated. Additionally, while the useof methyl methoxy propionate (MMP) has been proposed as utilizable forsolubilizing the TCU polymer and to address edge bead removingcharacteristics, MMP is not generally acceptable as a lithographicsolvent.

SUMMARY OF THE INVENTION

[0021] Therefore, it is an object of the present invention to provide anEBR compatible thermally curable polymer that is useful for an undercoatcomposition and layer thereof which avoids or reduces the aforementioneddrawbacks. Another object of this invention is to provide such athermally curable polymer to provide an undercoat layer which is curedat temperatures less than 250° C. and for a time of less than about 3minutes. It is a further object of this invention to provide anundercoat layer which is insoluble to the top resist's solvent system,minimizes reflectivity effects, and has an etch rate comparable tonovolaks.

[0022] Other and further objects, advantages and features of the presentinvention shall become apparent as described below.

[0023] The present invention is directed to an EBR compatible thermallycurable polymer composition comprising a novel hydroxyl-containingpolymer, an amino cross-linking agent and a thermal acid generator. Thethermally curable polymer composition may be dissolved in a solvent andused as an undercoat layer in deep UV lithography.

[0024] In addition, the present invention also relates to aphotolithographic coated substrate comprising: a substrate, a thermallycured undercoat composition on the substrate, and a radiation-sensitiveresist topcoat on the thermally cured undercoat composition.Furthermore, the present invention further relates to a process forusing the photolithographic coated substrate for the production ofrelief structures.

[0025] The polymers generally useful in accordance with this inventionwill have the general formula

[0026] wherein R¹ is H or methyl; R² is the substituted or unsubstitutedC₆-C₁₄ aryl acrylate or C₆-C₁₄ aryl methacrylate group wherein thesubstituted groups may be phenyl, C₁₋₄ alkyl or C₁₋₄ alkoxy; R³ ishydroxyl functionalized C₁-C₈ alkyl acrylate , methacrylate or C₆-C₁₄aryl group, R⁴ is a C₁-C₁₀ linear or branched alkylene; p is an integerof from 1 to 5 with the proviso that there are no more than thirtycarbon atoms in the [—R⁴O—]_(p) grouping; R⁵ is a C₁-C₁₀ linear,branched or cyclic alkyl, substituted or unsubstituted C₆-C₁₄ aryl, orsubstituted or unsubstituted C₇-C₁₅ alicyclic hydrocarbon; and m isabout 40 to 70, n is about 15 to 35, and o is about 15 to 25. Thepreferred mole percent ranges are m=60-68, n=15-20 and o=15-20 The arylgroups in the above mentioned definitions are preferably C₆-C₁₀ arylgroups, and more preferably phenyl groups. The molecular weight of thepolymers of this invention will generally range from about 8,000 toabout 100,000, preferably from about 10,000 to about 24, 000.

[0027] Components m, n and o impart absorption, solubility andcrosslinking functions when applied as a TCU material. Each monomericunit is focused on one of the three functions listed above, but may havesome impact on more than one function. This impact is dependent on thespecific monomer unit being employed. Changing the amount of monomerrepresented by m in the formula can vary plasma etch resistance andabsorbance, which will strongly vary the optical parameter k, whoseinfluence is on the reflection control of TCU material. The solubilityand etch resistance can be optimized by choosing appropriate comonomersn and o. The crosslinking rate is determined by the amount of monomerrepresented by n in the above formula. Generally, for 248 nmmicrolithography the optimum range of values for refractive index (n)and complex index (k) are about 1.56 to 1.76 and 0.125 to 0.275respectively

DETAILED DESCRIPTION AND EMBODIMENTS

[0028] In accordance with this invention we obtain such EBR compatiblethermally cured polymers by providing monomeric units in the polymerthat are designed to modify the solubility/absorbance characteristics.Preferably, such monomeric units are provided in the polymer from themonomers ethyleneglycol dicyclopenteneyl methacrylate (EGDCPMA) incombination with monomeric units of biphenyl methacrylate (BPMA) andhydroxystyrene (HS), that have the following three formulae:

[0029] In general the hydroxystyrene (HS) unit is provided by using themonomer acetoxystyrene (AcSt)

[0030] as the polymerization monomer in the polymerization reactionmixture and, after the polymerization reaction has taken place, dilutingthe reaction mixture with methanol and sodium methoxide in methanol(e.g., 10% solution) for methanolysis.

[0031] The phenolic OH functional group in PHS will be responsible forcross-linking reaction with a melamine or glycoluril type ofcross-linker and the ethylene glycol group in EGDCPMA and phenolicfunctional group in PHS may promote solubility in the ester-solventspolyethylene glycol mono methyl ether acetate (PGMEA), ethyl lactate(EL), ethyl ethoxy propionate (EEP) and the like. The absorbance at248-nm can be controlled through terpolymerization with acetoxystyreneby adjusting the ratio between biphenyl methacrylate, acetoxystyrene andthe ethylene glycol functionalized monomers

[0032] The thermally curable polymer composition comprises ahydroxyl-containing monomeric unit. Any suitable hydroxyl containingpolymer may be used such as polymers comprising monomer units ofhydroxystyrene, hydroxyalkyl acrylate or hydroxyalkyl methacrylate.Examples of suitable hydroxyalkyl acrylate or methacrylates monomerunits are 2-hydroxyethyl acrylate or methacrylate, 3-hydroxypropylacrylate or methacrylate, 4-hydroxybutyl acrylate or methacrylate,5-hydroxypentyl acrylate or methacrylate, and 6-hydroxyhexyl acrylate ormethacrylate and the like. Preferably, the hydroxyalkyl acrylate ormethacrylate monomer units contains primary hydroxyl groups, althoughsecondary and tertiary alcohol groups or mixtures of primary andsecondary or primary, secondary and tertiary alcohol groups may be used.Suitable examples of secondary alcohols are 2-hydroxypropyl acrylate ormethacrylate, 3-hydroxybutyl acrylate, 4-hydroxypentyl acrylate ormethacrylate, 5-hydroxyhexyl acrylate or methacrylate, and the like. Thepreferred hydroxyalkyl acrylate or methacrylate is 2-hydroxyethylacrylate or methacrylate.

[0033] The hydroxyl containing polymer should comprise aromatic monomerunits to balance n & k of the resist, preferably biphenyl acrylate ormethacrylate, naphthyl acrylate or methacrylate, and anthracenylacrylate or methacrylate. In addition, the thermally curable polymercomposition may also further comprise monomer units of ethylene glycolester of acrylic or methacrylic acid to make more soluble polymer.Suitable example of monomer units, ethylene glycol methyl ether acrylateand methacrylates, ethylene glycol phenyl ether acrylates andmethacrylates, diethylene glycol methyl ether acrylate and methacrylatesand the like. Preferably, polymers comprising units of hydroxystyrene,biphenyl methacrylate and 2-(dicyclopenteneyloxy) ether acrylates andmethacrylates have a number average molecular weight of about 8,000 to40,000, more preferably 10,000 to 24,000.

[0034] Suitable solvents for the undercoat include ketones, ethers andesters, such as 2-heptanone, cyclohexanone, propylene glycol monoethylether acetate, propylene glycol methyl ether acetate, methyl lactate,ethyl lactate, methyl 3-methoxypropionate, N-methyl-2-pyrrolidone,ethylene glycol monoisopropyl ether, diethylene glycol monoethyl ether,diethylene glycol dimethyl ether and the like.

[0035] This invention relates to an EBR compatible thermally curablepolymer composition, which may be used for forming an undercoat layer indeep UV lithography. The thermally curable polymer composition comprisesa hydroxyl-containing polymer, an amino cross-linking agent and athermal acid generator and solvent. When the composition is heated, thethermal acid generator generates an acid that protonates thepolyfunctional amino cross-linking agent resulting in a very strongelectrophilic group. This group reacts with a hydroxyl group on thehydroxyl-containing polymer forming a cured cross-linked polymer matrix.

[0036] Any suitable amino cross-linking agent may be used in the presentapplication such as methylolated and/or methylolated and etherifiedmelamines, methylolated and/or methylolated and etherified guanaminesand the like. The preferred amino cross-linking agents have the generalformula:

[0037] wherein Y is NR¹⁰R¹¹ or a substituted or unsubstituted C₆-C₁₄aryl or C₁-C₈ alkyl group; and R⁶ to R¹ ₁ are independently a hydrogenor a group of the formula —CH₂OH or —CH₂O R¹² wherein R¹² is an alkylgroup of about 1 to 8 carbons.

[0038] Examples of suitable melamine cross-linking agents aremethoxyalkylmelamines such as hexamethoxymethylmelamine,trimethoxymethylmelamine, hexamethoxyethylmelamine,tetramethoxy-ethylmelamine, hexamethoxypropylmelamine,pentamethoxypropylmelamine, and the like. The preferred melaminecross-linking agent is hexamethoxymethyl-melamine. Preferredaminocrosslinking agents are MW100LM melamine crosslinker from SanwaChemical Co. Ltd., Kanaxawa-ken, Japan, Cymel 303 and Powderlink fromCytec Industries, West Patterson, N.J.

[0039] The thermal acid generator of the present invention has thegeneral formula:

[0040] where R¹³ is a substituted or unsubstituted alkyl, cycloalkyl oraromatic group wherein the substituted group is a halogen, alkoxy,aromatic, nitro or amino group; and R¹⁴ to R¹⁸ are independentlyselected from hydrogen, linear or branched C₁ to C₄ alkyl, alkoxy,amino, alkylamino, aryl, alkenyl, halogen, acyloxy, cycloalkyl, orannulated cycloalkyl, aromatic or heterocyclic. The preferred thermalacid generators are cyclohexyl p-toluenesulfonate, menthylp-toluenesulfonate, bornyl p-toluenesulfonate, cyclohexyltriisopropylbenzenesulfonate, cyclohexyl 4-methoxybenzene sulfonate.More preferable thermal acid generators are cyclohexylp-toluenesulfonate, menthyl p-toluenesulfonate and cyclohexyl2,4,6-triisopropylbenzenesulfonate.

[0041] Annulated means that the cycloalkyl, aromatic or heterocyclicring is connected onto the benzene ring of the thermal acid generatorsuch as, for example, the annulated aromatic shown below

[0042] The thermal acid generators described above should not beconsidered photoacid generators. Any sensitivity that the thermal acidgenerators would have to UV light should be very poor, and they cannotpractically be used in photolithography as a photoacid generator.

[0043] The thermally curable polymer composition preferably contains, ona total solids basis, about 75 to 95 wt. %, and more preferably about 82to 95 wt. % of hydroxyl containing polymer. The amount of the aminocross-linking agent in the thermally curable polymer composition ispreferably about 3 to 20 wt. % and more preferably about 3 to 6 wt. %.The amount of the thermal acid generator in the thermally curablepolymer composition is preferably about 0.5 to 5 wt. % and morepreferably about 2 to 4 wt. %.

[0044] The thermally curable polymer composition of the presentinvention should not begin significant cross-linking until it reaches atemperature of about 50° C. Significant cross-linking below 50° C. maylead to gel formation at room temperature, which will reduce its shelflife. Gel formation results in non-uniform coatings and line widthvariations across the substrate when the thermally curable polymercomposition is used as an undercoat layer in microlithography.

[0045] The present invention also relates to a photolithographic coatedsubstrate comprising: a substrate, a thermally cured undercoatcomposition on the substrate, and a radiation-sensitive resist topcoaton the thermally cured undercoat composition. The thermally curedundercoat composition comprises the thermally curable polymercomposition that comprises a hydroxyl-containing polymer, an aminocross-linking agent and a thermal acid generator that has been heated toform a cross-linked matrix. Any of the polymers described above may beused as the hydroxyl-containing polymer.

[0046] The present invention further relates to a process for using thephotolithographic coated substrate for the production of reliefstructures comprising the steps of: providing the photolithographiccoated substrate, imagewise exposing the radiation-sensitive resisttopcoat to actinic radiation; and forming a resist image by developingthe radiation-sensitive resist topcoat with a developer to form openareas in the radiation-sensitive resist topcoat. In addition, thethermally cured undercoat composition may be removed in the open areasof the developed radiation-sensitive resist topcoat by any suitableprocess such as oxygen plasma etching to form an image in the thermallycured undercoat composition.

[0047] One advantage of the thermally curable polymer composition isthat it may be cured at a temperature of less than about 250° C. and fora time less than about 180 seconds. This makes it particularly useful asan undercoat layer for a resist system where temperature and timeconstraints are important for commercial viability. Preferably, thethermally curable polymer composition is cured at temperatures between150 to 250° C. and more preferably between temperatures of 180 to 220°C. The preferable cure times are from about 30 to 180 seconds and morepreferably from about 60 to 120 seconds.

[0048] Both the undercoat and the radiation-sensitive compositions areuniformly applied to a substrate by known coating methods. Thecompositions are solubilized in an organic solvent and the coatings maybe applied by spin-coating, dipping, knife coating, lamination,brushing, spraying, and reverse-roll coating. The coating thicknessrange generally covers values of about 0.1 to more than 10 μm and morepreferably from about 0.1 to 1.5 um for the radiation-sensitive resistand about 0.3 to 3.0 um for the undercoat layer. After the coatingoperation, the solvent is generally removed by curing or drying.

[0049] Suitable solvents for both the undercoat and topradiation-sensitive compositions include ketones, ethers and esters,such as methyl ethyl ketone, methyl isobutyl ketone, 2-heptanone,cyclopentanone, cyclehexanone, 2-methoxy-1-propylene acetate,2-methoxyethanol, 2-ethoxyethanol, 2-ethoxyethyl acetate,I-methoxy-2-propyl acetate, 1,2-dimethoxy ethane ethyl acetate,cellosolve acetate, propylene glycol monoethyl ether acetate, propyleneglycol methyl ether acetate, methyl lactate, ethyl lactate, methylpyruvate, ethyl pyruvate, ethyl 3-methoxypropionate,N-methyl-2-pyrrolidone, 1,4-dioxane, ethylene glycol monoisopropylether, diethylene glycol monoethyl ether, diethylene glycol monomethylether, diethylene glycol dimethyl ether, and the like. The solventsemployed in the undercoat and top photoresist compositions will bechosen with a view toward their compatibility with the polymer resin inthe undercoat and top photoresist compositions. For example, Thtchoiceof solvent for the photoresist composition and the concentration thereofdepends principally on the type of functionalities incorporated in theacid labile polymer, the photoacid generator, and the coating method.The solvent should be inert, should dissolve all the components in thephotoresist, should not undergo any chemical reaction with thecomponents and should be re-removable on drying after coating

[0050] The radiation-sensitive resist topcoat of the present inventionmay be any suitable radiation-sensitive resist. It is typically achemically amplified resist sensitive to radiation in the deep UV regionsuch as those discussed in U.S. Pat. Nos. 5,492,793 and 5,747,622.Preferably, for a bilayer resist system, the radiation-sensitive resistwill contain silicon to protect it from oxygen plasma etching.

[0051] The radiation-sensitive resist will also contain a photoacidgenerating (PAG) compound. The PAG compounds may be of any suitable typesuch as sulfonium or iodonium salts, nitrobenzyl esters, imidosulfonatesesters and the like. Typically, the PAG will be present in an amount ofabout 1 to 10% based on the weight of the polymer.

[0052] Any suitable photoacid generator compounds may be used in thephotoresist composition. The photoacid generator compounds are wellknown and include, for example, onium salts such as diazonium,sulfonium, sulfoxonium and iodonium salts, and disulfones. Suitablephotoacid generator compounds are disclosed, for example, in U.S. Pat.Nos. 5,558,978 and 5,468,589 which are incorporated herein by reference.

[0053] Suitable examples of photoacid generators are phenacylp-methylbenzenesulfonate, benzoin p-toluenesulfonate,α-(p-toluene-sulfonyloxy)methylbenzoin3-(p-toluenesulfonyloxy)-2-hydroxy-2-phenyl-1-phenylpropyl ether,N-(p-dodecylbenzenesulfonyloxy)-1 ,8-naphthalimide andN-(phenyl-sulfonyloxy)-1 ,8-napthalimide.

[0054] Other suitable compounds are o-nitrobenzaldehydes which rearrangeon actinic irradiation to give o-nitrosobenzoic acids such as1-nitrobenzaldehyde and 2,6-nitrobenzaldehyde, α-haloacylphenones suchas α,α,α-trichloroacetophenone andp-tert-butyl-α,α,α-trichloroacetophenone, and sulfonic esters ofo-hydroxyacylphenones, such as 2-hydroxybenzophenone methanesulfonateand 2,4-hydroxybenzophenone bis(methanesulfonate).

[0055] Still other suitable examples of photoacid generators aretriphenylsulfonium bromide, triphenylsulfonium chloride,triphenylsulfonium iodide, triphenylsulfonium hexafluorophosphate,triphenylsulfonium hexafluoroarsenate, triphenylsulfoniumhexafluoroarsenate, triphenylsulfonium trifluoromethanesulfonate,diphenylethylsulfonium chloride, phenacyldimethylsulfonium chloride,phenacyltetrahydrothiophenium chloride,4-nitrophenacyltetrahydrothiopheniumn chloride and4-hydroxy-2-methylphenylhexahydrothiopyrylium chloride.

[0056] Further examples of suitable photoacid generators for use in thisinvention are bis(p-toluenesulfonyl)diazomethane, methylsulfonylp-toluenesulfonyldiazomethane,1-cyclo-hexylsulfonyl-1-(1,1-dimethylethylsulfonyl)diazomethane,bis(1,1-dimethylethylsulfonyl)diazomethane,bis(1-methylethylsulfonyl)diazomethane,bis(cyclohexylsulfonyl)diazomethane,1-p-toluenesulfonyl-1-cyclohexylcarbonyld iazomethane,2-methyl-2-(p-toluenesulfony1)propiophenone,2-methanesulfonyl-2-methyl-(4-methylthiopropiophenone,2,4-methy1-2-(p-toluenesulfonyl)pent-3-one,1-diazo-1-methylsulfonyl-4-phenyl-2-butanone,2-(cyclohexylcarbonyl-2-(p-toluenesulfonyl)propane,1-cyclohexylsulfonyl-1cyclohexylcarbonyldiazomethane,1-diazo-1-cyclohexylsulfonyl-3,3-dimethyl-2-butanone,1-diazo-1-(1,1-dimethylethylsulfonyl)-3,3-dimethyl-2-butanone,1-acetyl-1-(1-methylethylsulfonyl)diazomethane,1-diazo-1-(p-toluenesulfonyl)-3,3-dimethyl-2-butanone,1-diazo-1-benzenesulfonyl-3,3-dimethyl-2-butanone,1-diazo-1-(p-toluenesulfonyl)-3-methyl-2-butanone, cyclohexyl2-diazo-2-(p-toluenesulfonyl)acetate, tert-butyl2-diazo-2-benzenesulfonylacetate,isopropyl-2-diazo-2-methanesulfonylacetate, cyclohexyl2-diazo-2-benzenesulfonylacetate, tert-butyl 2diazo-2-(p-toluenesulfonyl)acetate, 2-nitrobenzyl p-toluenesulfonate, 302,6-dinitrobenzyl p-toluenesulfonate, 2,4-dinitrobenzylp-trifluoromethylbenzenesulfonate.

[0057] Other suitable examples of photogenerators arehexafluorotetrabromo-bisphenol A,1,1,1-tris(3,5-dibromo-4-hydroxyphenyl)ethane andN-(2,4,6-tribromophenyl)-N′-(p-toluenesulfonyl)urea.

[0058] The photoacid generator compound is typically employed in theamounts of about 0.0001 to 20% by weight of polymer solids and morepreferably about 1% to 10% by weight of polymer solids.

[0059] In an additional embodiment, base additives may be added to thephotoresist composition. The purpose of the base additive is to scavengeprotons present in the photoresist prior to being irradiated by theactinic radiation. The base prevents attack and cleavage of the acidlabile groups by the undesirable acids, thereby increasing theperformance and stability of the resist. The percentage of base in thecomposition should be significantly lower than the photoacid generatorbecause it would not be desirable for the base to interfere with thecleavage of the acid labile groups after the photoresist composition isirradiated. The preferred range of the base compounds, when present, isabout 3% to 50% by weight of the photoacid generator compound. Suitableexamples of base additives are 2-methylimidazole, triisopropylamine,4-dimethylaminopryidine, 4,4′-diaminodiphenyl ether, 2,4,5 triphenylimidazole and 1,5-diazobicyclo[4.3.0]non-5-ene.

[0060] Dyes may be added to the photoresist to increase the absorptionof the composition to the actinic radiation wavelength. The dye must notpoison the composition and must be capable of withstanding the processconditions including any thermal treatments. Examples of suitable dyesare fluorenone derivatives, anthracene derivatives or pyrenederivatives. Other specific dyes that are suitable for photoresistcompositions are described in U.S. Pat. No. 5593812.

[0061] The photoresist composition may further comprise conventionaladditives such as adhesion promoters and surfactants. A person skilledin the art will be able to choose the appropriate desired additive andits concentration.

[0062] The invention further relates to a process for forming a patternon a substrate which comprises the following process steps: applicationof a photoresist coating comprising one of the compositions describedabove to the substrate; imagewise exposure of the coating to actinicradiation; treatment of the coating with an alkaline aqueous developeruntil the areas of the coating which have been exposed to the radiationdissolve from the substrate and an imaged photoresist structured coatingremains on the substrate.

[0063] For the production of relief structures, the radiation-sensitiveresist is imagewise exposed to actinic radiation. The term ‘imagewise’exposure includes both exposure through a photomask containing apredetermined pattern, exposure by means of any suitable source ofactinic radiation, such as for example, a computer controlled laser beamwhich is moved over the surface of the coated substrate, exposure bymeans of computer-controlled electron beams, and exposure by means ofX-rays or UV rays, through a corresponding mask. The imagewise exposuregenerates acid in the exposed regions of the resist which cleaves theacid labile groups resulting in a polymer which is aqueous soluble.Typically, after imagewise exposure, the chemically amplified resistwill be subjected to a post exposure heating treatment that virtuallycompletes the reaction of the photoacid generator with the acid labilegroups.

[0064] After imagewise exposure and any heat treatment of the material,the exposed areas of the top radiation-sensitive resist are typicallyremoved by dissolution in a aqueous developer. The choice of theparticular developer depends on the type of photoresist; in particularon the nature of the polymer resin or the photolysis products generated.The developer can comprise aqueous solutions of bases to which organicsolvents or mixtures thereof may have been added. Particularly preferreddevelopers are aqueous alkaline solutions. These include, for example,aqueous solutions of alkali metal silicates, phosphates, hydroxides andcarbonates, but in particular of tetra alkylammonium hydroxides, andmore preferably tetramethylammonium hydroxide (TMAH). If desired,relatively small amounts of wetting agents and/or organic solvents canalso be added to these solutions.

[0065] The radiation-sensitive resist used for the bilayer processdescribed above will typically contain silicon or have siliconincorporated into the resist after development. After images are formedin the radiation-sensitive resist, the substrate will be placed in anplasma-etching environment comprising oxygen so that the underlayercoating will be removed in the area unprotected by the resist. Thesilicon incorporated in the radiation-sensitive resist forms silicondioxide when exposed to an oxygen plasma and By protects the resist frombeing etched so that relief structures can be formed in the undercoatlayer.

[0066] After the oxygen plasma step, the substrate carrying the bilayerrelief structure is generally subjected to at least one furthertreatment step which changes the substrate in areas not covered by thebilayer coating. Typically, this can be implantation of a dopant,deposition of another material on the substrate or an etching of thesubstrate. This is usually followed by the removal of the resist coatingfrom the substrate typically by a fluorine/oxygen plasma etch.

[0067] The previously proposed copolymer comprising BPMA and HEMA isinsoluble in most of the EBR compatible solvents and lithographicsolvents such as PGMEA, EL and the like. The hydroxyl group of HEMA wasused as the crosslinking functional group. In the preferred terpolymerof the present invention, namely a terpolymer comprising BPMA, AcSt(which further methanolysed to p-hydroxystyrene (HS)) and EGDCPMA, theBPMA unit in the polymer contributes towards optimizing the n & k valueof the underlayer. The PHS unit in the polymer has two further roles inaddition to its roles of absorbance and plasma etch resistance. Itprovides the functionality for cross-linking which is more effectivethan the hydroxy functionality in HEMA. Secondly the HS as itsacetoxystyrene precursor copolymerizes randomly with BPMA, which changesthe block nature of BPMA in microstructure of polymer and enhance thesolubility of the polymer. The 3^(rd) monomer, an ester having at leastone ether linkage, enhances solubility of polymer and increase etchresistant of polymer. The present polymer system is compatible to EBRsolvents.

[0068] The present invention relates to a polymer composition comprisinga thermally crosslinkable group which is highly soluble in all EBRcompatible solvents. The present invention provides a thermally curablepolymer composition, which is useful for an undercoat layer in deep UVlithography. This undercoat layer polymer can be cured at temperatureless than about 220° C. and for a time less than about 2 minutes. Thisundercoat is insoluble to the top resist's solvent system and has anetch rate comparable to novolaks. The undercoat layer polymercomposition of this invention has an index of refraction (n & k) tunableby composition that can be optimized to minimize reflection at theimaging layer/underlayer interface, and where scumming and footing canbe completely eliminated by adjusting the amount of crosslinker in theformulation.

[0069] The invention is illustrated by, but not limited to, thefollowing examples in which the parts and percentages are by weightunless otherwise specified.

[0070] A general synthetic procedure used for obtaining polymers of thisinvention by polymerization in tetrahydrofuran is as follows.

[0071] The mixture of monomers, initiator and chain transfer agent wereare dissolved in 150 g THF under flow of N₂ in a round bottom flaskequipped with a reflux condenser and a gas inlet. The mixture was heatedto 65° C. with stirring and continued at the same temperature for 20 hunder N₂. After that, the reaction mixture was cooled down to roomtemperature and an aliquot was taken for GPC. The reaction mixture wasdiluted with 60 ml methanol and sodium methoxide in methanol (10%solution) was added to it for methanolysis. The mixture was refluxed andthe by-product methyl acetate was continuously removed by azeotropicdistillation using Dean-Stark trap for 4 h. After cooling down to roomtemperature, 20 g Amberlyst 15 resin (ion exchange resin available fromRohm & Haas) was added to the mixture to ion exchange of sodium andstirred for 3 h. The resin was filtered and the solution was slowlypoured into 4 L distilled water. The solid polymer was isolated byfiltration and redissolved in 300 ml THF. The polymer was precipitatedinto 2 L isopropanol. After filtration, the solid was dried at 60° C.for 24 h under vacuum.

[0072] The general analytical procedures employed were as follows.

[0073] Molecular weights and molecular weight distributions weremeasured using a Waters Corp. liquid chromatograph (refractive indexdetection, Millennium (GPC V software), equipped with the followingPhenogel-10, 7.8×250 mm columns: 10-4A, 500A & 50A (from Phenomena) andTHF eluent. Thermal decomposition measurements (TGA) were performedusing a Perkin-Elmer thermal gravimetric analyzer. The glass transitiontemperature (Tg) of the polymer was measured using Perkin-Elmer Pyris 1Differential Scanning Calorimeter at a heating rate of 10° C./minute.The structure and composition of polymer was analyzed by ¹³C NMR using aBruker 400 MHz NMR-spectrometer.

POLYMER EXAMPLE 1

[0074] The mixture of monomers [4-biphenyl methacrylate (72.37 g, 0.303mol), acetoxy styrene (10.56 g, 0.065 mol) and ethylene glycoldicyclopentenyl ether methacrylate (17.07 g, 0.065 mol)] and initiatorVAZO 67 (6.00 g, 6.0 wt % vs monomers) and chain transfer agent1-dodecanethiol (1.80 g, 30 wt % vs initiator) were polymerizedaccording to the general procedure above. Transesterification employed4.0 g sodium methoxide solution. Yield: 91.3 g, 94%. M_(w)=14,666;M_(w)/M_(n)=1.92. 5% weight loss at 310° C., Tg: 128° C. composition ofpolymers, mol %: 69% biphenyl methacrylate units; 16% hydroxystyreneunits and 15% ethyleneglycol dicyclopentenyl ether methacrylate units.

POLYMER EXAMPLE 2

[0075] The mixture of monomers [4-biphenyl methacrylate (62.74 g, 0.263mol), acetoxy styrene (14.23 g, 0.087 mol) and ethylene glycoldicyclopentenyl ether methacrylate (23.03 g, 0.087 mol)] and initiatorVAZO 67 (6.00 g, 6.0 wt % vs monomers) and chain transfer agent1-dodecanethiol (1.80 g, 30 wt % vs initiator) were polymerizedaccording to the general procedure above. Tranesterification employed5.0 g sodium methoxide solution. Yield: 91.5 g, 95%. M_(w)=13,715;M_(w)/M_(n)=1.97. TGA: 5% weight loss at 305° C.; Tg: 124° C.;composition of polymers, mol %: 60% biphenyl methacrylate units; 19%hydroxystyrene units and 21% ethyleneglycol dicyclopentenyl ethermethacrylate units.

POLYMER EXAMPLE 3

[0076] The mixture of monomers [4-biphenyl methacrylate (54.09 g, 0.227mol), acetoxy styrene (22.09 g, 0.136 mol) and ethylene glycoldicyclopentenyl ether methacrylate (23.82 g, 0.09 mol)] and initiatorVAZO 67 (6.00 g, 6.0 wt % vs monomers) and chain transfer agent1-dodecanethiol (1.80 g, 30 wt % vs initiator) were polymerizedaccording to the general procedure above. Transesterification employed6.0 g sodium methoxide solution. Yield: 85.5 g, 91%. M_(w)=11,262/1.88;M_(w)/M_(n)=1.88; TGA: 5% weight loss at 300° C.; Tg: 118° C.composition of polymers, mol %: 51% biphenyl methacrylate units; 28%hydroxystyrene units and 21% ethyleneglycol dicyclopentenyl ethermethacrylate units.

POLYMER EXAMPLE 4

[0077] The mixture of monomers [biphenyl methacrylate [BPMA](37.74 g;0.158 mol), acetoxy styrene (8.54 g; 0.0527 mol) and ethyleneglycoldicyclopentenyl ether methacrylate (13.82 g; 0.0527 mol) and chaintransfer agent, 1-dodecanethiol (1.08 g, 30 wt % of initiator) weredissolved in 83.6 g of PGMEA (propylene glycol methyl ether acetate)(40% of solid) under flow of N₂ in a 500 mL, round bottom flask equippedwith a reflux condenser and a gas inlet. The mixture was heated to 70°C. Then, VAZO 67® [free radical initiator, Dupont product,2,2′-azobis(2-methylbutyronitrile)] (3.6 g, 6 wt % of monomer used) in6.4 g of PGMEA was added slowly for 15 minutes to the reaction mixtureand stirred for 24 h under N₂. The disappearance of BPMA was monitoredby GPC using a UV detector at 254 nm. After 24 h, residual BPMA was<0.1%. The reaction mixture was cooled to room temperature. Then, 2.0 gof sodium methoxide in methanol (10 wt %) and 50 ml methanol were addedto the flask. The reaction mixture was refluxed for 3 h and about 25 mlof methanol was removed by azeotropic distillation using a Dean-Starktrap. The solution was then cooled to room temperature and 10.0 g ofAmberlyst 15 resin was added to it. The reaction mixture was stirred for2h and the resin was isolated by filtration. The solution was distilledto half of the volume under vacuum <60° C. to remove methanol andby-product, propylene glycol methyl ether. Finally, a 30 wt % of solidsolution was made by adding PGMEA to it. M_(w)=15,700; M_(w)/M_(n)=1.95;and composition of polymers, mol %: 59% biphenyl methacrylate units; 20%hydroxystyrene units and 21% ethyleneglycol m dicyclopentenyl ethermethacrylate units.

POLYMER EXAMPLE 5

[0078] The mixture of monomers [biphenyl methacrylate [BPMA](37.74 g;0.158 mol), acetoxy styrene (8.54 g; 0.0527 mol) and ethyleneglycoldicyclopentenyl ether methacrylate (13.82 g; 0.0527 mol) and chaintransfer agent, 1-dodecanethiol (1.08 g, 30 wt % of initiator) weredissolved in 83.6 g of PGMEA (propylene glycol methyl ether acetate)(40% of solid) under flow of N₂ in a 500 mL, round bottom flask equippedwith a reflux condenser and a gas inlet. The mixture was heated to 70°C. Then, VAZO 67® [free radical initiator, Dupont product,2,2′-azobis(2-methylbutyronitrile)] (3.6 g, 6 wt % of monomer used) in6.4 g of PGMEA was added slowly for 15 minutes to the reaction mixture.Then, the temperature was slowly increased to 80° C. and stirred for 4 hunder N₂. The disappearance of BPMA was monitored by GPC using a UVdetector at 254 nm. After 3 h, residual BPMA was <0.1%. The mixture wascooled to room temperature. Then, 2.0 g of sodium methoxide in methanol(10 wt %) and 50 ml methanol were added to the flask. The reactionmixture was refluxed for 3 h and about 25 ml of methanol was removed byazeotropic distillation using a Dean-Stark trap. The solution was thencooled to room temperature and 10.0 g of Amberlyst 15 resin was added toit. The reaction mixture was stirred for 2h and the resin was separatedby filtration. The solution was distilled to half of the volume undervacuum <60° C. to remove methanol and by-product, propylene glycolmethyl ether. Finally, a 30 wt % of solid solution was made by addingPGMEA to it. removed by azeotropic distillation using Dean-Stark trap.M_(w)=11,044; M_(w)/M_(n)=2.11 and composition of polymers, mol %: 60%biphenyl methacrylate units; 19% hydroxystyrene units and 21%ethyleneglycol dicyclopentenyl ether methacrylate units.

[0079] Undercoat formulations of the polymers of Examples 1 to 5 wereformulated in the following examples.

Undercoat Formulation 1

[0080] For 100 g of undercoat solution (total 15 weight % solids), 14.02g of Polymer of Example 1, 4.0 g MW100LM (Melamine crosslinker, SanwaChemical Co. Ltd., Kanaxawa-ken, Japan) solution (20 wt % solution inPGMEA) and 1.875 g of cyclohexyl tosylate thermal acid generatorsolution (20 wt % solution in PGMEA) were combined and dissolved in 80.1g of propylene glycol methyl ether acetate (PGMEA). The mixture(polymer/crosslinker/TAG=93.5/4.0/2.5%) was rolled overnight, and theundercoat solution was filtered twice through a 0.1 μm Teflon filter.

[0081] Undercoat Formulation 2

[0082] For 100 g of undercoat solution (total 15 weight % solids), 14.02g of Polymer of Example 2, 4.0 g MW100LM crosslinker solution (20 wt %solution in PGMEA) and 1.875 g of cyclohexyl tosylate thermal acidgenerator solution (20 wt % solution in PGMEA) were combined anddissolved in 80.1 g of propylene glycol methyl ether acetate (PGMEA).The mixture (polymer/crosslinker/TAG=93.5/4.0/2.5%) was rolledovernight, and the undercoat solution was filtered twice through a 0.1μm Teflon filter.

Undercoat Formulation 3

[0083] For 100 g of undercoat solution (total 15 weight % solids), 14.02g of Polymer of Example 3, 4.0 g MW100LM crosslinker solution (20 wt %solution in PGMEA) and 1.875 g of cyclohexyl tosylate thermal acidgenerator solution (20 wt % solution in PGMEA) were combined anddissolved in 80.1 g of propylene glycol methyl ether acetate (PGMEA).The mixture (polymer/crosslinker/TAG=93.514.0/2.5%) was rolledovernight, and the undercoat solution was filtered twice through a 0.1μm Teflon filter.

Undercoat Formulation 4

[0084] For 100 g of undercoat solution (total 15 weight % solids), 46.75g of Polymer of Example 4 solution, 4.0 g MW100LM crosslinker solution(20 wt % solution in PGMEA) and 1.875 g of cyclohexyl tosylate thermalacid generator solution (20 wt % solution in PGMEA) were combined anddissolved in 47.4 g of propylene glycol methyl ether acetate (PGMEA).The mixture (polymer/crosslinker/TAG=93.5/4.0/2.5%) was rolledovernight, and the undercoat solution was filtered twice through a 0.1μm Teflon filter.

Undercoat Formulation 5

[0085] For 100 g of undercoat solution (total 15 weight % solids), 46.75g of Polymer of Example 5 solution, 4.0 g MW100LM crosslinker solution(20 wt % solution in PGMEA) and 1.875 g of cyclohexyl tosylate thermalacid generator solution (20 wt % solution in PGMEA) were combined anddissolved in 47.4 g of propylene glycol methyl ether acetate (PGMEA).The mixture (polymer/crosslinker/TAG=93.5/4.0/2.5%) was rolledovernight, and the undercoat solution was filtered twice through a 0.1μm Teflon filter.

Undercoat Formulation 6

[0086] For 100 g of undercoat solution (total 15 weight % solids), 14.33g of Polymer of Example 1, 2.0 g MW100LM crosslinker solution (20 wt %solution in PGMEA) and 1.875 g of cyclohexyl tosylate thermal acidgenerator solution (20 wt % solution in PGMEA) were combined anddissolved in 81.8 g of propylene glycol methyl ether acetate (PGMEA).The mixture (polymer/crosslinker/TAG=95.5/2.0/2.5%) was rolledovernight, and the undercoat solution was filtered twice through a 0.1μm Teflon filter.

Undercoat Formulation 7

[0087] For 100 g of undercoat solution (total 15 weight % solids), 14.18g of Polymer of Example 1, 3.0 g MW100LM crosslinker solution (20 wt %solution in PGMEA) and 1.875 g of cyclohexyl tosylate thermal acidgenerator solution (20 wt % solution in PGMEA) were combined anddissolved in 81.0 g of propylene glycol methyl ether acetate (PGMEA).The mixture (polymer/crosslinker/TAG=94.5/3.0/2.5%) was rolledovernight, and the undercoat solution was filtered twice through a 0.1μm Teflon filter.

Undercoat Formulation 8

[0088] For 100 g of undercoat solution (total 15 weight % solids), 13.83g of Polymer of Example 1, 6.0 g MW100LM crosslinker solution (20 wt %solution in PGMEA) and 1.875 g of cyclohexyl tosylate thermal acidgenerator solution (20 wt % solution in PGMEA) were combined anddissolved in 78.4 g of propylene glycol methyl ether acetate (PGMEA).The mixture (polymer/crosslinker/TAG=91.5/6.0/2.5%) was rolled 1Rovernight, and the undercoat solution was filtered twice through a 0.1μm Teflon filter.

Undercoat Formulation 9

[0089] For 100 g of undercoat solution (total 15 weight % solids), 13.13g of Polymer of Example 1, 10.0 g MW100LM crosslinker solution (20 wt %solution in PGMEA) and 1.875 g of cyclohexyl tosylate thermal acidgenerator solution (20 wt % solution in PGMEA) were combined anddissolved in 75.0 g of propylene glycol methyl ether acetate (PGMEA).The mixture (polymer/crosslinker/TAG=87.5/10.0/2.5%) was rolledovernight, and the undercoat solution was filtered twice through a 0.1μm Teflon filter.

Undercoat Formulation 10

[0090] For 100 g of undercoat solution (total 15 weight % solids), 14.02g of Polymer of Example 1, 4.0 g Powderlink crosslinker solution (20 wt% solution in PGMEA) and 1.875 g of cyclohexyl tosylate thermal acidgenerator solution (20 wt % solution in PGMEA) were combined anddissolved in 80.1 g of propylene glycol methyl ether acetate (PGMEA).The mixture (polymer/crosslinker/TAG=93.5/4.0/2.5%) was rolledovernight, and the undercoat solution was filtered twice through a 0.1μm Teflon filter.

Undercoat Formulation 11

[0091] For 100 g of undercoat solution (total 15 weight % solids),14.1Og of Polymer: Example 1, 4.0 g MW100LM crosslinker solution (20 wt% solution in PGMEA) and 1.5 g of cyclohexyl tosylate thermal acidgenerator solution (20 wt % solution in PGMEA) were combined anddissolved in 80.4 g of propylene glycol methyl ether acetate (PGMEA).The mixture (polymer/crosslinker/TAG=94.014.0/2.0%) was rolledovernight, and the undercoat solution was filtered twice through a 0.1μm Teflon filter.

Undercoat Formulation 12

[0092] For 100 g of undercoat solution (total 15 weight % solids), 13.95g of Polymer of Example 1, 4.0 g MW100LM crosslinker solution (20 wt %solution in PGMEA) and 2.25 g of cyclohexyl tosylate thermal acidgenerator solution (20 wt % solution in PGMEA) were combined anddissolved in 79.8 g of propylene glycol methyl ether acetate (PGMEA).The mixture (polymer/crosslinker/TAG=93.0/4.0/3.0%) was rolledovernight, and the undercoat solution was filtered twice through a 0.1μm Teflon filter.

Undercoat Formulation 13

[0093] For 100 g of undercoat solution (total 15 weight % solids), 13.80g of Polymer of Example 1, 4.0 g MWl OOLM crosslinker solution (20 wt %solution in PGMEA) and 3.0 g of cyclohexyl tosylate thermal acidgenerator solution (20 wt % solution in PGMEA) were combined anddissolved in 79.2 g of propylene glycol methyl ether acetate (PGMEA).The mixture (polymer/crosslinker/TAG=93.0/4.0/4.0%) was rolledovernight, and the undercoat solution was filtered twice through a 0.1μm Teflon filter.

Undercoat Formulation 14

[0094] For 100 g of undercoat solution (total 15 weight % solids), 13.65g of Polymer of Example 1, 4.0 g MW100LM crosslinker solution (20 wt %solution in PGMEA) and 3.75 g of cyclohexyl tosylate thermal acidgenerator solution (20 wt % solution in PGMEA) were combined anddissolved in 78.6 g of propylene glycol methyl ether acetate (PGMEA).The mixture (polymer/crosslinker/TAG=91.0/4.0/5.0%) was rolledovernight, and the undercoat solution was filtered twice through a 0.1μm Teflon filter.

[0095] The general procedure employed for lithographic testing theundercoat formulations was as follows.

[0096] A silicon wafer was spincoated with undercoat from an undercoatformulation and baked at 205° C. for 90 see to yield a 0.50 μm thickfilm. The imaging layer (TIS 2000, a chemically amplified resistavailable from Arch Chemicals, Inc Norwalk, Conn.) was spincoated overthe undercoat and baked at 135° C. for 1 min to yield a 0.25 μm thickfilm. The coated wafer was then patternwise exposed using an Ultratech248 nm Stepper. The wafer was post exposure baked at 125° C. for 1 minand puddle developed for 60 sec in 0.262 N aqueous TMAH. The wafer wasrinsed with Dl water and spun dry. The patterns were analyzed byscanning electron microscopy (SEM). Images from SEM showed the bilayerresist could resolve features as small as 0.13 μM.

[0097] The general lithographic performance of the TIS-2000 compositionsof this invention was:

[0098] photo speed range: 30 to 40 (mJ/cm²);

[0099] resolution range: 0.120 to 0.130 (μm), and

[0100] depth of focus: 0.70 to 1.0 (0.130μm features).

[0101] The results of the lithographic testing of the composition is setforth in the following Table 1. TABLE 1 Summary of the Formulations andImage Quality Evaluation of the Undercoat Formulations. ResolutionIsolated lines Cross- Thermal acid (0.13 ?m), Cross- linker Generatorresist/under- Poly- Polymer linking (grams) (grams) PGMEA coat (IL/UL)Example mer (grams) Agent 20 wt % solid 20 wt % solid (grams) interfacequality 1 Poly- 14.02 MW100 4.0 1.875 80.1 No footing at mer 1 LM IL/ULinterface 2 Poly- 14.02 MW100 4.0 1.875 80.1 No Footing at mer 2 LMIL/UL interface 3 Poly- 14.02 MW100 4.0 1.875 80.1 Scumming at mer 3 LMIL/UL interface 4 Poly- 14.02 MW100 4.0 1.875 80.1 No Footing at mer 4LM IL/UL interface 5 Poly- 14.02 MW100 4.0 1.875 80.1 No Footing at mer5 LM IL/UL interface 6 Poly- 14.33 MW100 2.0 1.875 81.8 Collapsed mer 1LM line patterns 7 Poly- 14.18 MW100 3.0 1.875 81.0 Footing mer 1 LM 8Poly- 13.83 MW100 6.0 1.875 78.4 No Footing at mer 1 LM IL/UL interface9 Poly- 13.13 MW100 10.0 1.875 75.0 Footing mer 1 LM 10 Poly- 14.02Powder 4.0 1.875 80.1 No Footing at mer 1 link IL/UL interface 11 Poly-14.10 MW100 4.0 1.5 80.4 No Footing at mer 1 LM IL/UL interface 12 Poly-13.95 MW100 4.0 2.25 79.8 No Footing at mer 1 LM IL/UL interface 13Poly- 13.80 MW100 4.0 3.0 79.2 No Footing at mer 1 LM IL/UL interface 14Poly- 13.65 MW100 4.0 3.75 78.6 T-topping mer 1 LM

[0102] SEM's result showed that there was scumming or foot at theresist/undercoat interface in the formulations with high cross-linkingsite (hydroxy styrene) polymer. Similarly, SEM'S result showed collapsedline patterns at low concentration of melamine crosslinker, perhaps dueto insufficient curing of undercoat, which leads to intermixing at theresist/undercoat interface. Scum formation and footed profiles wereobserved at higher concentrations of crosslinker used in theformulations.

[0103] While the invention has been described herein with reference tothe specific embodiments thereof, it will be appreciated that changes,modification and variations can be made without departing from thespirit and scope of the inventive concept disclosed herein. Accordingly,it is intended to embrace all such changes, modification and variationsthat fall with the spirit and scope of the appended claims.

We claim:
 1. A hydroxyl-containing polymer comprising units m, n and oof the following formula:

wherein R¹ is selected from the group consisting of H or methyl; R² isselected from the group consisting of a substituted or unsubstitutedC₆-C₁₄ aryl acrylate or C₆-C₁₄ aryl methacrylate group wherein thesubstituted groups may be phenyl, C₁₋₄ alkyl or C₁₋₄ alkoxy; R³ isselected from the group consisting of hydroxyl functionalized C₁-C₈alkyl acrylate, methacrylate or C₆-C₁₄ aryl group, R⁴ is a C₁-C₁₀ linearor branched alkylene; p is an integer of from 1 to 5 with the provisothat there are no more than thirty carbon atoms in the [—R⁴O—-]_(p); R⁵is selected from the group consisting of C₁-C₁₀ linear, branched orcyclic alkyl, substituted or unsubstituted C₆-C₁₄ aryl, or substitutedor unsubstituted C₇-C₁₅ alicyclic hydrocarbon; and m is about 40 to 70,n is about 15 to 35, and o is about 15 to
 25. 2. A polymer according toclaim 1 wherein unit m is a biphenyl-acrylate or methacrylate unit andR⁵ is dicyclopentenyl.
 3. A polymer according to claim 1 wherein unit nis a hydroxystyrene unit and R⁵ is dicyclopentenyl.
 4. A polymeraccording to claim 1 wherein unit m is a biphenyl-acrylate ormethacrylate unit; unit n is a hydroxystyrene unit; and unit o is anethylene glycol dicyclopenteneyl-acrylate or methacrylate unit.
 5. Apolymer according to claim 4 wherein the o unit is an ethylene glycoldicyclopenteneyl methacrylate unit and unit m is a biphenyl methacrylateunit.
 6. A polymer according to claim 4 having a molecular weight offrom about 10,000 to about 24,000.
 7. A thermally curable polymercomposition comprising a hydroxyl-containing polymer, an aminocross-linking agent and a thermal acid generator, wherein thehydroxyl-containing polymer is a polymer comprising units m, n and o ofthe following formula:

wherein R¹ is selected from the group consisting of H or methyl; R² isselected from the group consisting of a substituted or unsubstitutedC₆-C₁₄ aryl acrylate or C₆-C₁₄ aryl methacrylate group wherein thesubstituted groups may be phenyl, C₁₋₄ alkyl or C₁₋₄ alkoxy; R³ isselected from the group consisting of hydroxyl functionalized C₁-C₈alkyl acrylate, methacrylate or C₆-C₁₄ aryl group, R⁴ is a C₁-C₁₀ linearor branched alkylene; p is an integer of from 1 to 5 with the provisothat there are no more than thirty carbon atoms in the [—R⁴O—]_(p); R⁵is selected from the group consisting of C₁-C₁₀ linear, branched orcyclic alkyl, substituted or unsubstituted C₆-C₁₄ aryl, or substitutedor unsubstituted C₇-C₁₅ alicyclic hydrocarbon; and m is about 40 to 70,n is about 15 to 35, and o is about 15 to
 25. 8. A composition accordingto claim 7 wherein unit m is a biphenyl-acrylate or methacrylate unitand R⁵ is dicyclopentenyl.
 9. A composition according to claim 7 whereinunit n is a hydroxystyrene unit and R⁵ is dicyclopentenyl.
 10. Acomposition according to claim 9 wherein unit m is a biphenyl-acrylateor methacrylate unit; unit n is a hydroxystyrene unit; and unit o is anethylene glycol dicyclopenteneyl-acrylate or methacrylate unit.
 11. Acomposition according to claim 9 wherein the o unit is a n ethyleneglycol dicyclopenteneyl methacrylate unit and the m unit is a biphenylmethacrylate unit.
 12. A composition according to claim 5 wherein thehydroxyl-containing polymer has a molecular weight of from about 10,000to about 24,000.
 13. A photolithographic sensitive coated substratecomprising: (a) a substrate, (b) a thermally cured undercoat on saidsubstrate, and (c) a radiation-sensitive resist topcoat on saidundercoat, wherein said thermally cured undercoat comprises a thermallycured composition comprising a hydroxyl-containing polymer, an aminocross-linking agent and a thermal acid generator, and wherein thehydroxyl containing polymer is a polymer comprising units m, n and o ofthe following formula:

wherein R¹ is selected from the group consisting of H or methyl; R² isselected from the group consisting of a substituted or unsubstitutedC₆-C₁₄ aryl acrylate or C₆-C₁₄ aryl methacrylate group wherein thesubstituted groups may be phenyl, C₁₋₄ alkyl or C₁₋₄ alkoxy; R³ isselected from the group consisting of hydroxyl functionalized C₁-C₈alkyl acrylate , methacrylate or C₆-C₁₄ aryl group, R⁴ is a C₁-C₁₀linear or branched alkylene; p is an integer of from 1 to 5 with theproviso that there are no more than thirty carbon atoms in the[—R⁴O—]_(p); R⁵ is selected from the group consisting of C₁-C₁₀ linear,branched or cyclic alkyl, substituted or unsubstituted C₆-C₁₄ aryl, orsubstituted or unsubstituted C₇-C₁₅ alicyclic hydrocarbon; and m isabout 40 to 70, n is about 15 to 35, and o is about 15 to
 25. 14. Acoated substrate according to claim 13 wherein unit m is abiphenyl-acrylate or methacrylate unit and R⁵ is dicyclopentenyl.
 15. Acoated substrate according to claim 13 wherein unit n is ahydroxystyrene unit and R⁵ is dicyclopentenyl.
 16. A coated substrateaccording to claim 13 wherein unit m is a biphenyl-acrylate ormethacrylate unit; unit n is a hydroxystyrene unit; and unit o is aethylene glycol dicyclopenteneyl-acrylate or methacrylate unit.
 17. Acoated substrate according to claim 16 wherein the o unit is an ethyleneglycol dicyclopenteneyl methacrylate unit and unit m is a biphenylmethacrylate unit.
 18. A coated substrate according to claim 16 whereinthe hydroxyl-containing polymer has a molecular weight of from about10,000 to about 24,000.
 19. A process for the production of reliefstructures comprising the steps of: (a) forming a coated substratewherein the coated substrate comprises (1) a substrate, (2) a thermallycured undercoat on said substrate, and (2) a radiation-sensitive resisttopcoat on said undercoat, wherein said thermally cured undercoatcomprises a thermally cured composition comprising a hydroxyl-containingpolymer, an amino cross-linking agent and a thermal acid generator, andwherein the hydroxyl containing polymer is a polymer comprising units m,n and o of the following formula:

wherein R¹ is selected from the group consisting of H or methyl; R² isselected from the group consisting of a substituted or unsubstitutedC₆-C₁₄ aryl acrylate or C₆-C₁₄ aryl methacrylate group wherein thesubstituted groups may be phenyl, C₁₋₄ alkyl or C₁₋₄ alkoxy; R³ isselected from the group consisting of hydroxyl functionalized C₁-C₈alkyl acrylate, methacrylate or C₆-C₁₄ aryl group, R⁴ is a groupcontaining an alicyclic ether moiety containing 6 or more carbon atomsC₁-C₁₀ linear or branched alkylene; p is an integer of from 1 to 5 withthe proviso that there are no more than thirty carbon atoms in the[—R⁴O—]_(p); R⁵ is selected from the group consisting of C₁-C₁₀ linear,branched or cyclic alkyl, substituted or unsubstituted C₆-C₁₄ aryl, orsubstituted or unsubstituted C₇-C₁₅ alicyclic hydrocarbon; and m isabout 40 to 70, n is about 15 to 35, and o is about 15 to 25; (b)imagewise exposing said radiation-sensitive topcoat to actinicradiation; and (c) forming a resist image by developing saidradiation-sensitive topcoat with a developer.
 20. A process according toclaim 19 wherein unit m is a biphenyl-acrylate or methacrylate unit andR⁵ is dicyclopentenyl.
 21. A processs according to claim 19 wherein unitn is a hydroxystyrene unit and R⁵ is dicyclopentenyl.
 22. A processaccording to claim 19 wherein unit m is a biphenyl-acrylate ormethacrylate unit; unit n is a hydroxystyrene unit; and unit o is anethylene glycol dicyclopenteneyl-acrylate or methacrylate unit.
 23. Aprocess according to claim 22 wherein the o unit is an ethylene glycoldicyclopenteneyl methacrylate unit and unit m is a biphenyl methacrylateunit.
 24. A process according to claim 22 wherein thehydroxyl-containing polymer has a molecular weight of from about 10,000to about 24,000.